Select name when renaming a notebook

The default notebook name is `Untitled<x>`. It is unlikely the user will want to
keep this name or part of it. Instead, select the text in the input field when renaming, so the
user can easily type over the name and change it.

To test this change, create a new notebook, then click on the title "Untitled0" or similar to rename it. Instead of the cursor waiting at the end of the line, the text field should be selected, for easier changing.